This repository includes the files necessary to implement a Java program which will serve as a concurrency example.
The main objective of the program is to perform an efficient concurrency program where the instances of the class Monkey have to share an instance of the class Rope to cross a canyon.
The program allows the user to insert in the command line an argument to select how many instances of the class Monkey are going to be created (there will be 8 by default).
Example: java Monkey_Problem 3 will start the program creating and running only 3 instances of the class Monkey.
The program starts by asking the user if they want to use the version with the colourised output (or the standard one).
The first version of this repository contains the java classes:
- Main.java: Main function to create the instances of the different classes and to start the Threads that will run during this concurrency exercise.
- Rope.java: Rope class that contains the methods to cross the Rope. It also contains the conditions and functions to handle concurrency.
- Monkey.java: The Monkey class that implements Runnable will perform different actions using the methods of the class Rope.
- Canyon.java: Auxiliary class to visualize the threads' (monkeys) state.
- CanyonColorized.java: Extends Canyon class. Prints a colourised output.
The repository contains a Script to test the program.
We want to know if African monkeys can be taught about deadlocks. She locates a deep canyon and fastens a rope across it, so the monkeys can cross hand-over-hand. Passage along the rope follows these rules:
- Several monkeys can cross at the same time, provided that they are all going in the same direction.
- If eastward moving and westward moving monkeys ever get onto the rope at the same time, a deadlock will result (the monkeys will get stuck in the middle) because it is impossible for one monkey to climb over another one while suspended over the canyon.
- If a monkey wants to cross the canyon, he must check to see that no other monkey is currently crossing in the opposite direction.
- Your solution should avoid starvation. When a monkey that wants to cross to the east arrives at the rope and finds monkeys crossing to the west, the monkey waits until the rope in empty, but no more westward moving monkeys are allowed to start until at least one monkey has crossed the other way. For this exercise, you are to write a program to simulate activity for this canyon crossing problem:
- Simulate each monkey as a separate process.
- Altogether, a lot of monkeys, whatever you want, will cross the canyon, with a random number generator specifying whether they are eastward moving or westward moving.
- Use a random number generator, so the time between monkey arrivals is between 1 and 8 seconds.
- Each monkey takes 1 second to get on the rope. (That is, the minimum inter-monkey spacing is 1 second.)
- All monkeys travel at the same speed. Each traversal takes exactly 4 seconds, after the monkey is on the rope.
The approach adopted for this problem was using intrinsic locks or Monitors to enforce the exclusive access to the instance Rope and to guarantee that the intances of the class Monkey follow the requirements indicated in the description of the problem (considering the order of execution for each Thread and their interruptions) as well as the proper function of the concurrency program avoiding Dead Locks and Starvation.
Being Threads the basic unit of execution for concurrent programming in the Java programming language the instances of the class Monkey are Runnable objects (Implements Runnable). Here you can find my other repository for this same exercise in Scala: https://github.com/Gares95/Monkey_Problem_Scala
Here you can see a Diagram representing the Guarded Block implemented in the program with the conditions in the class Rope.
Here you can see an example of the resulted output after running this concurrency program (running only 5 instances of the class monkey or threads).
Here you can see an example of the output using the colorized version.
